I will however impart some wisom my boxing coach showed me once. People familiar with boxing will have run into this, but for those that haven't:

In the clinch you put your head on one of thier shoulders and generally look away slightly. Usually this happens when you are tired. Try to get an overhook on the side arm your have YOUR head resting on.

Here is the technique:

Imagine you have your opponents head resting on your right shoulder and you have overhooked his right arm with your left arm. In one short quick movement you ram your shoulder upwards QUICKLY, and then step back slightly and hit him with your left hook. When done correctly his head will be popped up and jaw exposed with no cover on that side because your left arm was blocking his right side. You have a beautifull shot. Once they are familiar with this you can be sure you won't get the opportunity again - so make sure when you do it you really slam that hook home.

yrkoon, I'm gonna try that tonight at sparring. Hopefully, the opponent isn't more than 5" taller than me (all the heavier guys have fights coming up)

The only time I've personally seen shoulders used is in kickboxing when a fighter pushed away his opponent while clinching, then followed up with a barrage of kicks while the other guy was still moving backwards.

In MMA competitions, I've seen fighters try to shove their shoulders into their opponent's face to smother them or drive it in to do damage (not much damage done).

1) Is it possible to damage people using shoulders, actually slamming your shoulder(s) onto their bodies?

Yes. Ask any football player to confrim this.

2) Is it effective for MMA purposes?

Not in any significant way. To do any significant damage would require one to put their shoulder down and run, or at the very least, lunge powerfully, at the opponent. Running at your opponent while bent over=a good way to get KTFO.
I'm not sure enough power would be derived simply from body movement with the feet planted.

Here is the technique:

Imagine you have your opponents head resting on your right shoulder and you have overhooked his right arm with your left arm. In one short quick movement you ram your shoulder upwards QUICKLY, and then step back slightly and hit him with your left hook. When done correctly his head will be popped up and jaw exposed with no cover on that side because your left arm was blocking his right side. You have a beautifull shot. Once they are familiar with this you can be sure you won't get the opportunity again - so make sure when you do it you really slam that hook home.

A very effective technique against inexperienced boxers. Sometimes even works against experienced boxers, but I doubt it would be so effective in MMA. The reason this works so well in boxing is because of the ability we have to rest in the clinch with no fear of being taken down. I'm not a MMA fighter, but I doubt that resting like that in the clinch is very common.

I was using my shoulder against a guy sparring last night. Not so much as a 'strike' by itself to do the main damage, but using with footwork to split and take his center, control his upper body, occupy his space and throw off balance, to set up inside strikes, knees and takedown.

Based solely on Asia's Baji demonstration , I would say that using shoulders are effective in fighting, but I wouldn't necessarily use them to cause damage like a punch or a kick, but to unbalance or a create space so that I could perform a harder technique.

in mma sometimes you will see a fighter drive their shoulder into their opponents face, while in their full or half guard. they only do this because their hands are tied up, and they aren't allowed to headbutt.

and the technique Yrkoon9 brought up is pretty common in boxing. i could only see it working in boxing though.